1. Technical Field
The present invention relates to a dual polarized dipole antenna and to an antenna system comprising such antennas.
2. Description of the Prior Art
Dual polarized dipole antennas are well known in the art. They are often used in base station antenna systems for wireless communication systems, such as GSM, GPRS, EDGE, UMTS, LTE, LTE Advanced and WiMax systems. In these wireless systems they are often used in base station antenna arrays. The polarization employed in these types of antennas may be circular, elliptical or linear.
These types of antenna have two dipoles arranged such that the antenna radiates in two different polarizations. In its simplest form each dipole is made up of a two wire transmission line which is driven by a radio signal source in one end and an open circuit on the other end. There are also dipoles which are etched on a Printed Circuit Board (PCB) layer/substrate with dipole pattern etching.
A recent trend in the art is to use more broadband antennas in order to give an increased flexibility for deployments with regard to frequency bands without increasing the number of antenna units. For example, the previously used 1710-2170 MHz band antennas are today replaced by 1710-2690 MHz band antennas. This trend creates new technical challenges, e.g., the need of antenna elements with more bandwidth (i.e. ˜45% versus previously ˜25%; bandwidth of the element; that is, operation of, for example, bandwidth=(fmax−fmin/0.5(fmax+fmin)) and/or methods to get more bandwidth out of prior art designs.
A prior art dual polarized antenna (Master of Science Thesis: “Design of a broadband antenna element for LTE base station antennas” by Marie Ström, 2009 Chalmers University of Technology, Sweden) is comprised of two, on a PCB layer, printed dipoles mounted orthogonally to each other. Each of the printed dipoles also has associated parasitic element printed on the PCB to increase the bandwidth of the antenna. The parasitic element is printed on a PCB above the dipole pattern.